Bile duct ligation in the pig results in ulceration of the pars oesophagea (oesophagogastric junction) within 48 h with 100% reproducibility. This work describes novel observations made during development of such ulcers using an endoscope introduced at intervals postoperatively via a Thomas gastric cannula. Macroscopic and histological changes were recorded and compared with quantitative and qualitative changes in crude mucus scrapings and purified mucins. Crude mucus scrapings of the cardiac gland region had a higher protein content in the ulcerated states than in the normals. After bile duct ligation, the (degraded) mucin glycopeptide/total protein ratio was higher in partially purified mucus from pre-ulcerated and ulcerated stomachs as compared with normal samples. The quantity of purified mucin was less in samples from ulcerated stomachs, and the N-acetylgalactosamine and fucose contents were also decreased. It is possible that these changes resulted in the failure of the mucus barrier and the development of oesophagogastric junction ulceration.